Method for producing thin films by low temperature plasma-enhanced chemical vapor deposition using a rotating susceptor reactor

ABSTRACT

A method for depositing a film on a substrate by plasma-enhanced chemical vapor deposition at temperatures substantially lower than conventional thermal CVD temperatures comprises placing a substrate within a reaction chamber and exciting a first gas upstream of the substrate to generate activated radicals of the first gas. The substrate is rotated within the deposition chamber to create a pumping action which draws the gas mixture of first gas radicals to the substrate surface. A second gas is supplied proximate the substrate to mix with the activated radicals of the first gas and the mixture produces a surface reaction at the substrate to deposit a film. The pumping action draws the gas mixture down to the substrate surface in a laminar flow to reduce recirculation and radical recombination such that a sufficient amount of radicals are available at the substrate surface to take part in the surface reaction. Another method utilizes a gas-dispersing showerhead that is biased with RF energy to form an electrode which generates activated radicals and ions in a concentrated plasma close to the substrate surface. The activated plasma gas radicals and ions utilized in the invention contribute energy to the surface reaction such that the film may be deposited at a substantially lower deposition temperature that is necessary for traditional thermal CVD techniques. Furthermore, the activation of these species reduces the temperature needed to complete the surface reaction. The method is particularly useful in depositing titanium-containing films at low temperatures.

This application is a divisional of application Ser. No. 08/720,621filed on Oct. 2, 1996, entitled METHOD FOR PRODUCING THIN FILMS BY LOWTEMPERATURE PLASMA-ENHANCED CHEMICAL VAPOR DEPOSITION USING A ROTATINGSUSCEPTOR REACTOR, now U.S. Pat. No. 5,716,870, which application is, inturn, a divisional of application Ser. No. 08/253,393 filed on Jun. 3,1994, of Robert F. Foster et al., entitled METHOD AND APPARATUS FORPRODUCING THIN FILMS BY LOW TEMPERATURE PLASMA-ENHANCED CHEMICAL VAPORDEPOSITION USING A ROTATING SUSCEPTOR REACTOR, now U.S. Pat. No.5,665,640, which applications are completely incorporated herein byreference in their entireties.

FIELD OF THE INVENTION

This invention relates generally to plasma-enhanced chemical vapordeposition (PECVD) for applying a film coating to a substrate, and morespecifically to PECVD conducted at a low effective depositiontemperature at the substrate surface. Even more specifically, theinvention relates to deposition of titanium-containing films using lowtemperature CVD.

BACKGROUND OF THE INVENTION

In the formation of integrated circuits (IC's), thin films containingmetal and metalloid elements are often deposited upon the surface of asubstrate, such as a semiconductor wafer. Thin films are deposited toprovide conductive and ohmic contacts in the circuits and between thevarious devices of an IC. For example, a desired thin film might beapplied to the exposed surface of a contact or via hole on asemiconductor wafer, with the film passing through the insulative layerson the wafer to provide plugs of conductive material for the purpose ofmaking interconnections across the insulating layers.

One well known process for depositing thin metal films is chemical vapordeposition (CVD) in which a thin film is deposited using chemicalreactions between various deposition or reactant gases at the surface ofthe substrate. In CVD, reactant gases are pumped into proximity to asubstrate inside a reaction chamber, and the gases subsequently react atthe substrate surface resulting in one or more reaction by-productswhich form a film on the substrate surface. Any by-products remainingafter the deposition are removed from the chamber. While CVD is a usefultechnique for depositing films, many of the traditional CVD processesare basically thermal processes and require temperatures in excess of1000° C. in order to obtain the necessary reactions. Such a depositiontemperature is often far too high to be practically useful in ICfabrication due to the effects that high temperatures have on variousother aspects and layers of the electrical devices making up the IC.

Particularly, certain aspects of IC components are degraded by exposureto the high temperatures normally related to traditional thermal CVDprocesses. For example, at the device level of an IC, there are shallowdiffusions of semiconductor dopants which form the junctions of theelectrical devices within the IC. The dopants are often initiallydiffused using heat during a diffusion step, and therefore, the dopantswill continue to diffuse when the IC is subjected to a high temperatureduring CVD. Such further diffusion is undesirable because it causes thejunction of the device to shift, and thus alters the resultingelectrical characteristics of the IC. Therefore, for certain IC devices,exposing the substrate to processing temperatures of above 800° C. isavoided, and the upper temperature limit may be as low as 650° C. forother more temperature sensitive devices.

Furthermore, such temperature limitations may become even more severe ifthermal CVD is performed after metal interconnection or wiring has beenapplied to the IC. For example, many IC's utilize aluminum as aninterconnection metal. However, various undesirable voids and extrusionsoccur in aluminum when it is subjected to high processing temperatures.Therefore, once interconnecting aluminum has been deposited onto an IC,the maximum temperature to which it can be exposed is approximately 500°C., and the preferred upper temperature limit is 400° C. Therefore, asmay be appreciated, it is desirable during CVD processes to maintain lowdeposition temperatures whenever possible.

Consequently, the upper temperature limit to which a substrate must beexposed precludes the use of some traditional thermal CVD processeswhich might otherwise be very useful in fabricating IC's. A good exampleof one such useful process is the chemical vapor deposition of titanium.Titanium is typically used to provide ohmic contact between the siliconcontacts of an IC device and a metal interconnection. Titanium may bedeposited from TiBr₄, TiCl₄ or TiI₄ by using CVD methods such asunimolecular pyrolysis or hydrogen reduction. However, the temperaturesnecessary for these thermal processes are in excess of 1000° C., andsuch a deposition temperature is much to high to be practically usefulin IC fabrication. Therefore, the deposition of titanium andtitanium-containing films presents a problem in formation of integratedcircuits.

There are low temperature physical techniques available for depositingtitanium on temperature sensitive substrates. Sputtering is one suchtechnique involving the use of a target of layer material and an ionizedplasma. To sputter deposit a film, the target is electrically biased andions from the plasma are attracted to the target to bombard the targetand dislodge target material particles. The particles then deposit themselves cumulatively as a film upon the substrate. Titanium may besputtered, for example, over a silicon substrate after various contactsor via openings are cut into a level of the substrate. The substratemight then be heated to about 800° C. to allow the silicon and titaniumto alloy and form a layer of titanium silicide (TiSi₂). After thedeposition of the titanium layer, the excess titanium is etched awayfrom the top surface of the substrate leaving TiSi₂ at the bottom ofeach contact or via. A metal interconnection is then deposited directlyover the TiSi₂.

While physical sputtering provides deposition of a titanium film at alower temperature, sputtering processes have various drawbacks.Sputtering normally yields very poor step coverage. Step coverage isdefined as the ratio of film thickness on the bottom of a contact on asubstrate wafer to the film thickness on the sides of the contact or thetop surface of the substrate. Consequently, to sputter deposit apredetermined amount of titanium at the bottom of a contact or via, alarger amount of the sputtered titanium must be deposited on the topsurface of the substrate or the sides of the contact. For example, inorder to deposit a 200 Å film at the bottom of a contact usingsputtering, a 600 Å to 1000 Å film layer may have to be deposited ontothe top surface of t he substrate or the sides of the contact. Since theexcess titanium has to be etched away, sputtering is wasteful and costlywhen depositing layers containing titanium.

Furthermore, the step coverage of the contact with sputtering techniquesdecreases as the aspect ratio of the contact or via increases. Theaspect ratio of a contact is defined as the ratio of contact depth tothe width of the contact. Therefore, a thicker sputtered film must bedeposited on the top or sides of a contact that is narrow and deep (highaspect ratio) in order to obtain a particular film thickness at thebottom of the contact than would be necessary with a shallow and widecontact (low aspect ratio). In other words, for smaller devicedimensions in an IC, corresponding to high aspect ratio contacts andvias, sputtering is even more inefficient and wasteful. The decreasedstep coverage during sputter deposition over smaller devices results inan increased amount of titanium that must be deposited, thus increasingthe amount of titanium applied and etched away, increasing the titaniumdeposition time, and increasing the etching time that is necessary toremove excess titanium. Accordingly, as IC device geometries continue toshrink and aspect ratios increase, deposition of titanium-containinglayers by sputtering becomes very costly.

On the other hand, using a CVD process for depositing atitanium-containing film layer may be accomplished with nearly 100% stepcoverage. That is, the film thickness at the bottom of the contact wouldapproximately equal the thickness on the top surface almost regardlessof the aspect ratio of the contact or via being filled. However, asdiscussed above, the temperatures necessary for such CVD processes aretoo high and would degrade other aspects of the IC. Consequently, itwould be desirable to achieve titanium CVD at a temperature less than800° C., and preferably less than 650° C. Further, it is generallydesirable to reduce the deposition temperature for any CVD process whichis utilized to deposit a film in IC fabrication.

One approach which has been utilized in CVD processes to lower thereaction temperature is to ionize one or more of the reactant gases.Such a technique is generally referred to as plasma enhanced chemicalvapor deposition (PECVD). While it has been possible with such anapproach to somewhat lower the deposition temperatures, the highsticking coefficient of the ionized plasma particles degrades the stepcoverage of the film. That is, ions of the reactant gases are highlyreactive and have a tendency to contact and stick to the walls of thevias or contacts in the substrate. The ion particles do not migratedownwardly to the bottom surface of the contact where the coating isdesired but rather non-conformally coat the sides of the contact. Thisresults in increased material usage, deposition times and etch times.Therefore, PECVD using ionized reactant gases has not been a completelyadequate solution to lowering traditional high CVD temperatures andachieving good step coverage and film conformality.

Additionally, when using a CVD process to apply a film, it is desirableto uniformly deposit the film. To do so, such as to apply a uniform filmof tungsten (W), for example, a uniform supply of reactant gases must besupplied across the surface of the substrate and the spent gases andreaction by-products should be removed from the surface being coated. Inthis respect, prior art CVD processes have again performed with limitedsuccess. Specifically, in known CVD processes, turbulence in the flow ofreaction gases inhibits the efficiency and uniformity of the coatingprocess and aggravates the deposition and migration of contaminantswithin the reaction chamber. In tungsten CVD processes, tungstenhexafluoride (WF₆) is employed as a reactant gas. Tungsten hexafluorideis very costly and thus, when reactant gas utilization efficiency islow, as it is in prior art CVD processes, the overall process costs aresignificantly increased. Accordingly, there is a need for CVD processeswhich have improved gas flow and reduced gas flow turbulence to moreefficiently and more uniformly supply reaction gases to and removereaction by-products from the surfaces of the substrate being coated.

Therefore, CVD processes which may be accomplished at lower effectivetemperatures are desired. It is further desirable to have a lowtemperature deposition which provides good step coverage. It is stillfurther desirable to have a PECVD process which produces uniform filmthickness and effective utilization of reactant gases. Accordingly, thepresent invention addresses these objectives and the shortcomings of thevarious CVD and PECVD processes currently available. Further, thepresent invention, particularly addresses the difficulties associatedwith depositing titanium and titanium-containing films using CVD.

SUMMARY OF THE INVENTION

The CVD apparatuses and methods of the present invention overcome orobviate the high temperature and gas flow drawbacks associated with manyof the currently available thermal CVD and PECVD apparatuses andprocesses. Specifically, the present invention achieves deposition of atitanium-containing film at a substantially lower temperature ascompared to traditional thermal CVD processes. Further, in doing so, theinvention does not compromise the conformality of the resulting filmlayer, and makes efficient use of the activated and reactant gases whilereducing gas turbulence at the substrate surface.

The low temperature deposition of the present invention is accomplishedin two alternative methods. The first method utilizes the upstream,remote generation of a plasma. The plasma is pumped down to a substrateby a rotating susceptor and is extinguished as it travels to thesubstrate, so that predominantly activated gas radicals are present. Thegas radicals combine with unexcited reactant gases to deposit a filmlayer on the substrate by CVD techniques. The pumping of the rotatingsusceptor minimizes gas particle recirculations and collisions to yielda useful percentage of radicals.

The second method utilizes an RF showerhead design which yields aconcentrated plasma very close to the substrate surface. All of thegases, both plasma and reactant gases, are passed through the RFshowerhead electrode and are excited. Since the susceptor acts asanother electrode, the RF showerhead and the susceptor form a parallelplate electrode configuration. With the RF electrode method, the plasmagases utilized in the chemical vapor deposition at the substratecontains a mixture of both ions and radicals which contribute energy tothe surface reaction.

More specifically, one CVD process of the present invention utilizes aplasma source to generate, upstream of a substrate wafer, a gas plasmacontaining various excited particles of the gas, including charged ionsand excited, charge-neutral radicals, as well as free electrons. Theexcited particles of the plasma gas, and predominantly the excitedradical particles are brought to the surface before they have had achance to combine to form neutral molecules. The excited radicalschemically react with one or more reactant gases to form a thin film ona substrate. The excited radicals supply energy to the surface reactionsuch that CVD may be used in accordance with the principles of thepresent invention at temperatures substantially lower than thoserequired with traditional CVD methods.

To prevent the particle sticking and the reduced layer conformalityassociated with traditional PECVD using ionized particles, the upstreammethod of the present invention utilizes predominantly charge-neutral,activated radicals at the substrate surface which yield conformal,uniform films. However, the lifetime of such activated gas radicals isshort as they seek to recombine into a low energy, stable molecularstructure. As mentioned above, the present invention provides efficientuse of the activated gas radicals by bringing the radicals to thesubstrate surface before a significant number of them are able torecombine to form the original, stable gas molecules. For efficientdelivery of the radicals, the present invention utilizes a rotatingsusceptor which supports and rotates the substrate and creates adownward pumping action in the direction of the substrate. The rotatingsusceptor pumps the radicals to the substrate surface.

A reactant gas or gases are introduced into the deposition region abovethe substrate surface to mix with the activated gas radicals. Thedownward pumping action of the rotating susceptor simultaneously drawsthe mixture of radicals and reactant gases toward the substrate surface.At the substrate surface, the mixture of radicals and reactant gasesflows radially outward from the center of the substrate in asubstantially uniform laminar flow pattern and the excited radicalsreact with the reactant gas particles in a surface reaction whichresults in a film layer being deposited upon the substrate surface.

The activated radicals supply energy to the surface reaction and therebyreduce the required energy, such as thermal energy, that is necessaryfor the chemical reaction to take place at the substrate surface.Therefore, the deposition takes place at a substantially lowertemperature than the temperature required by traditional CVD processes.For example, the deposition of a titanium-containing layer using thepresent invention may be accomplished at 600° C. or below versus 1000°C. for some traditional thermal CVD processes.

The unique pumping action and laminar flow of gases created by therotating susceptor ensures a useful density of radicals at the substratesurface. For example, by using a gas flow of between 500 to 50,000 sccm(standard cubic centimeters per minute), a susceptor rotation-rate of 0to 1,000 rpm, a reaction chamber pressure between 0.5 and 10 Torr, and areactant gas flow rate between 1 to 20 sccm, the present invention hasyielded thin films from CVD techniques at temperatures below 650° C. Theupstream plasma may be excited using either an RF signal or a microwavesignal. Accordingly, the invention has been found to yield desirableresults when the plasma is excited at frequencies as high as 2.54 GHzand as low as 13.56 kHz.

The laminar pattern created by the rotating susceptor minimizes gasparticle recirculations and subsequent radical recombinations at thesubstrate surface, and therefore, there are more activated radicalsavailable at the substrate surface for the low temperature CVD process.Additionally, in the method of the present invention, increasing therotation rate of the susceptor increases the deposition rate at thesubstrate surface. Due to the unique combination of activated radicalsand the laminar flow produced by the pumping action of the rotatingsusceptor, the deposition rate of the present invention increases beyondwhat might be achieved solely due to the increase in molecular reactantsat the substrate surface resulting from an increased pumping action.That is, increasing the rotation rate of the susceptor accomplishes morethan merely drawing reactant gases toward the substrate at a higherrate; it further minimizes recombination of radicals thus providing moreavailable radicals at the substrate surface. This enhancement in thedelivery of radicals to the substrate surface is an importantadvancement in PECVD processes. It allows the majority of the radicalsformed upstream or remotely from the substrate to be carried to thesubstrate surface so that they take place in the surface depositionreaction without a large amount of radical recombination loss. Thisenhancement and the subsequent increased energy at the surface reaction,in turn, allows the reaction to take place at even lower depositiontemperatures.

For the RF electrode plasma generation method of the present invention,the plasma gas is delivered proximate the surface of the substrateutilizing a gas-dispersing showerhead which is biased with RF energy toact as an electrode. A susceptor supporting a substrate acts as anotherparallel electrode. The RF showerhead/electrode generates a concentratedplasma very close to the surface of the substrate while a gas deliverycylinder attached to the showerhead ensures uniform gas flow to theplasma. The proximity of the plasma to the substrate ensures an ampledensity of activated radicals and ions for the surface reaction. Thatis, a combination of both gas radicals and gas ions is utilized in theRF showerhead/electrode method. Utilizing the showerhead/electrode, aspacing of less than 1" between the generated plasma and the substrateis possible yielding desirable CVD films. Furthermore, the RFshowerhead/electrode method keeps the plasma concentrated below theshowerhead and close to the substrate for efficient deposition. The RFshowerhead has been utilized at RF frequencies from 13.56 MHZ to as lowas 450 KHz.

While the present invention may be utilized with a number of differentplasma gases and reactant gases, the invention has been found to beparticularly useful for depositing titanium-containing films, such aspure titanium (Ti), titanium nitride (TiN) and/or titanium silicide(TiSi₂) films onto a substrate utilizing plasma containing radicals andions of hydrogen and nitrogen and/or disassociated titaniumtetrachloride (TiCl₄) and ammonia (NH₃). A diluent such as argon mightbe mixed with the plasma gas. Further, different plasma gases besidesH₂, N₂ and NH₃ might be used in accordance with the principles of thepresent invention to supply radicals and ions to the surface reactionaccording to the present invention.

In a specific embodiment, the invention has been found useful fordepositing titanium films over aluminum layers on a substrate.Deposition temperatures in accordance with the invention are low enoughthat the aluminum layer is not damaged by reflow during the deposition.

In another specific embodiment, the invention has been found useful forproducing selective deposition of titanium over a substrate having afield oxide (silicon oxide) layer patterned with vias into a lowersilicon layer. Under certain conditions, it has been found that titaniumdeposits only on the silicon layers in the vias without significantdeposition on the field oxide.

In accordance with various hardware embodiments of the invention, theplasma may be created using energy from various energy sources includingmicrowave and radio frequency (RF) sources. One hardware embodimentutilizes a showerhead/electrode which is biased with RF energy to createa plasma. One possible upstream plasma embodiment utilizes acommercially available plasma source with an RF coil surrounding aplasma region. Still another embodiment utilizes an upstream microwaveplasma source which remotely excites a plasma with microwave energy. Theremote plasma is then pumped along a tube whereby activated radicals areformed. After exiting the tube and entering the deposition chamber, theradicals are mixed with reactant gases and drawn to the substratesurface by the rotating susceptor.

The invention and the particular advantages and features of the presentinvention will now be described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view and partial cross-section of one embodiment of anupstream plasma-enhanced deposition chamber used to practice the methodsof the present invention using microwave energy.

FIG. 1A is a view of an alternative embodiment of an upstreamplasma-enhanced deposition chamber using microwave energy.

FIG. 2 is a side view and partial cross-section of one embodiment of adeposition chamber used to practice the methods of the present inventionusing an RF showerhead/electrode.

FIG. 2A is a more detailed view of the configuration of FIG. 2.

FIG. 2B is an alternative embodiment of the configuration of FIG. 2.

FIG. 3 is a side view an d partial cross-section of a second embodimentof an upstream plasma-enhanced deposition chamber using RF energy.

FIGS. 4A and 4B are Arrhenius function graphs of the necessaryactivation energy for deposition with and without the upstream activatedradicals of the present invention, respectively.

FIG. 5 are graphs of deposition rate increase as a function of rotationrate increase with and without the upstream activated radicals,respectively.

FIG. 6 is a photomicrograph showing selective deposition of titaniumfilms onto vias patterned in a silicon oxide layer overlying a siliconsubstrate.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes both methods and apparatuses foraccomplishing low temperature CVD utilizing activated gas radicalsand/or activated gas radicals and ions. Proper use of the activated ionsand radicals, and a resultant low temperature CVD method, requires auseful density of radicals and/or ions at the substrate surface. Arotating susceptor is used in accordance with the present inventionwhich rotates a substrate inside of a deposition chamber and drawsactivated gas radicals down to the surface of the substrate. Theradicals and reactant gases take part in a surface reaction on thesubstrate to deposit a film. The activated, charge-neutral radicals andcharged ions contribute energy to the surface reaction such that thefilm is deposited upon the substrate surface in a chemical vaportechnique at substantially lower temperatures than are possible withthermal CVD techniques. Also, because the ions and radicals areactivated by the plasma, less thermal energy is required to complete thesurface reaction.

Preferably, in the upstream plasma generation, predominantly radicalsare present at the substrate surface to participate in the lowtemperature surface reaction. The laminar gas flow created by thesusceptor reduces collisions and the subsequent recombinations of theactivated radicals into stable molecules so that a useful density of theradicals are delivered to the substrate surface to take place in thesurface reaction and subsequent film formation. With the RFshowerhead/electrode method, the plasma may be generated very close tothe substrate, as discussed further hereinbelow, thus enhancing theefficient use of the activated ions and radicals. The present inventionyields a CVD technique that may be accomplished at very low temperaturescompared with the traditional thermal CVD techniques thus making itpractical for integrated circuit fabrication requiring low depositiontemperatures. Furthermore, the inventive method achieves improved stepcoverage and film conformality over sputter deposition techniques andother CVD techniques. The invention may be utilized to deposit variousdifferent films by a low temperature CVD; however, it is particularlyuseful in depositing titanium-containing films such as titanium nitride(TiN) at low temperatures and especially pure titanium metal.

FIG. 1 shows one embodiment of an upstream plasma source with a rotatingsusceptor for practicing the upstream plasma-enhanced CVD of the presentinvention. The embodiment of FIG. 1 utilizes a microwave plasma sourcefor generating an upstream reactant gas plasma from which the necessaryactivated radicals are drawn. A reactor 5 includes a chamber housing 10enclosing a reaction space 12. The housing 10 may be controllablyvacuumed to a desired internal deposition pressure for practicing theinvention. Plasma gases to be excited, such as, for example, hydrogengas (H₂), nitrogen gas (N₂), and/or ammonia (NH₃) are introduced intospace 12 through a quartz tube 14. Plasma tube 14 is L-shaped and has along portion 16 which extends generally horizontally until it reaches a90° bend 15. After the 90° bend 15, a small straight section 18 extendsvertically downward and has an outlet end 19 which opens into space 12.Housing 10 also contains a rotating susceptor 20 which rotates on ashaft 21 coupled to a motor (not shown), such that the speed of therotation may be adjusted. Susceptor 20 supports a substrate 22 in thereaction space 10. A temperature control device (not shown) is coupledto susceptor 20 which is used to heat substrate 22 to the desiredtemperature. An example of a suitable reactor, including a rotatingsusceptor, for practicing the methods of the invention is the RotatingDisk Reactor available from Materials Research Corporation (MRC) ofPhoenix, Ariz.

A microwave energy source 24 is coupled to plasma tube 14 through amicrowave waveguide 26. The waveguide 26 propagates microwave energy 27from source 24 to tube 14 to define an excitation region 28 within thetube 14. Plasma gases are introduced into tube 14 at end 13 and travelalong the length of the tube 14 passing through region 28, wherein themicrowave energy 22 is absorbed by the gases to excite the gases to forma plasma. The plasma generated in tube 14 contains various activatedparticles including ions and activated, charge-neutral radicals. Forexample, if hydrogen gas (H₂) is introduced into tube 14, a hydrogenplasma containing free electrons (e⁻), hydrogen ions (H⁺) andcharge-neutral, activated hydrogen radicals (H*) is produced, whilenitrogen gas (N₂) yields electrons, nitrogen ions (N⁻) and activatedradicals (N*). Ammonia gas (NH₃) might also be utilized to produceradicals of hydrogen H* and nitrogen N*. However, as discussed ingreater detail below, NH₃ reacts with some reactant gases, such as(TiCl₄), to form an undesired adduct. Therefore, preferably pure H₂and/or N₂ are excited and utilized to achieve low temperature CVD.

Utilizing hydrogen (H₂) as the plasma gas, generation of the plasmaresults in generation of radicals H* as well as ionization as follows:

    H.sub.2 →2H.sup.+ +2e.sup.-  (ionization)           (EQ 1)

As the excited gas plasma travels along the horizontal section of tube34, recombination occurs according to equation 2 below as the plasma isextinguished, and additional hydrogen radicals H* are created through acombination of hydrogen ions and free electrons.

    H.sup.+ +e.sup.- →H* (recombination)                (EQ 2)

As time progresses, a second recombination may occur according toequation 3. The second recombination yields inactive, stable hydrogengas molecules which will not contribute reaction energy to the surfacereaction. Therefore, it is important to deliver the activated radicalsto a surface 23 of substrate 22 before they recombine.

    H*+H*→H.sub.2                                       (EQ 3)

The hydrogen radicals H* and any other remaining gas particles of theplasma travel around the 90° bend 15 of the tube 14 and are drawndownwardly along vertical section 18 and out into the reaction space 12through outlet 19 by the rotation of susceptor 20. Rotating susceptor 20generates a downward pumping action in the direction of substrate 22.The pumping action creates a laminar flow of gases over the wafersurface 23 as illustrated by arrows 29.

Preferably, susceptor 20 is operated to achieve matched gas flowconditions. In a matched gas flow, the rate of gas flow in a downwarddirection indicated by Q-1 equals the rate of gas flow in a horizontaldirection designated by Q-2. When these two gas flow rates are equal,matched flow occurs. An additional discussion of matched flow isdisclosed in the application entitled "A Method For Chemical VaporDeposition Of Titanium-Nitride Films At Low Temperatures", Ser. No.08/131,900, filed Oct. 5, 1993, now U.S. Pat. No. 5,378,501, whichapplication is incorporated herein by reference.

For an efficient CVD reaction according to the principles of the presentinvention, it is desirable that the plasma gas reaching the substrate 22contain a large percentage of radicals, and preferably 80% or moreactivated radicals by composition. Such a high radical compositionrequires drawing the plasma gas down to the substrate 22 with minimalrecombinations. Maximum utilization of radicals is accomplished by thelaminar flow created by the rotating susceptor 20. It has beendetermined through experimentation that the laminar flow pattern of thesusceptor 20 minimizes the recirculations of the gas reactants andparticularly minimizes recirculation of the activated gas radicals atthe substrate surface 23. The minimized recirculation, in turn,minimizes gas phase collisions of the activated radicals, and hence,reduces the rate at which the radicals recombine to form stablemolecules. That is, the amount of recombination of H* into H₂ accordingto equation 3 above is reduced. As a result, there is a greater densityof useful activated radicals available at the substrate surface 23 tosupply energy to the chemical surface reaction and to reduce the thermalenergy required in the chemical vapor deposition of the film. Thereby,the present invention effectively reduces the deposition temperature.

When gas radicals are introduced into space 12, the reactant gases areintroduced such as through a vertically adjustable showerhead 30 shownin FIG. 1. For example, to deposit a titanium-containing film, atitanium tetrahalide gas such as titanium tetrachloride (TiCl₄),titanium tetrabromide (TiBr₄), or titanium tetraiodide (TiI₄), andpreferably TiCl₄, is introduced. For a pure titanium layer, H₂ might beexcited into a plasma and TiCl₄ might be introduced into the reactionspace 12. A mixture of H* and TiCl₄ might then occur in space 12generally above susceptor 20 and substrate 22. The pumping action ofsusceptor 20 would draw the mixture down to substrate surface 23 in alaminar flow and the activated H* and TiCl₄ should react at surface 23to deposit a thin film on the substrate 22. Hydrogen radicals H* shouldsupply energy to the surface reaction according to equation 4.

    4H*+TiCl.sub.4 →Ti+4HCl                             (EQ 4)

The reaction should yield a film of titanium (Ti) upon the substratesurface 23 and hydrochloric acid (HCl) which might be removed throughthe appropriate exhaust port 32. The energy contributed to the reactionof equation 4 by the activated radicals should achieve a CVD film atreduced deposition temperatures.

While the example of the invention described hereinabove might yield alayer of pure titanium upon the substrate 22, various other materiallayers might also be deposited according to the principles of thepresent invention containing titanium or containing other desirableelements. For example, titanium nitride (TiN) might be deposited byintroducing hydrogen (H₂) and nitrogen (N₂) into the plasma-generatingtube 14 to yield H* and N* radicals. Further, ammonia gas (Nh₃) may beexcited and disassociated into a plasma containing H* and N* radicals.Similar to the recombination of the hydrogen gas plasma particles, theN* radicals will eventually combine into nitrogen molecules (N₂) unlessquickly drawn down to the surface of the substrate 23. As a furtherexample, titanium silicide (TiSi₂) might also be deposited according tothe principles of the present invention. In such a case, silane gas(SiH₄) might be introduced with the titanium-containing gas (e.g. TiCl₄)into the reaction space 12. Additionally, tungsten (W) may be depositedusing the apparatus of FIG. 1 and the method described. Examples ofchemical reactions for producing titanium nitride and titanium silicideare given below in equations 5 and 6, respectively.

    TiCl.sub.4 +N*+4H*→TiN+4HCl                         (EQ 5)

    TiCl.sub.4 +2SiH.sub.4 +4H*→TiSi.sub.2 +4HCl+4H.sub.2(EQ 6)

The microwave plasma deposition apparatus of FIG. 1 was used to deposita layer of tungsten and several tests were made to determine theviability of the method. Hydrogen was passed through quartz tube 14. Anexcited plasma was ignited in the vicinity of region 28 and traveleddownstream through tube 14 into reaction space 12. As the plasmatraveled along quartz tube 14, it was extinguished downstream of themicrowave excitation region 28 indicating that recombination of theexcited plasma particles had occurred, such as according to equation 2above to yield additional hydrogen radicals. The hydrogen radicals weresubsequently drawn down to substrate surface 23 by rotating susceptor20. Simultaneously, tungsten hexafluoride (WF₆) was introduced through agas port 29. A deposition reaction occurred according to Equation 7,below, to deposit a layer of tungsten onto substrate 22.

    WF.sub.6 +6H*→W+6HF                                 (EQ 7)

To verify that hydrogen radicals were actually reaching the substratesurface 23 and contributing to the CVD process, an activation energycomparison was made. Specifically, the tungsten deposition rate wasmeasured as a function of substrate temperature. The measurements weremade both with the microwave power turned off and no plasma and with themicrowave power turned on to create a plasma and hydrogen radicals. Thedata measured is shown plotted in FIGS. 4A and 4B as a logarithmicArrhenius function, i.e., plotted as In (k) versus 1/T, where k is thereaction rate constant and T is absolute temperature. The process anddeposition parameters for both the non-plasma and plasma depositionsillustrated by FIGS. 4A and 4B, respectively, were as follows:

H₂ rate=2,000 sccm

WF₆ rate=225 sccm

Pressure =4 Torr

Rotation rate of susceptor=30 RPM

A Microwave Power=900 Watts

From the experiments, and the resulting Arrhenius functions, theactivation energy, E_(a), was calculated. For the thermal process, thatis, with the microwave power turned off, E_(a) =67.1 kJ/mole-degree K.However, when the microwave power was turned on to create a plasma, theactivation energy necessary for the deposition process was only E_(a)=63.2 kJ/mole-degree K. The decrease in activation energy E_(a) betweenthe plasma and non-plasma deposition processes, indicates that activatedhydrogen radicals are reaching the substrate surface and participatingin the surface reaction according to the principles of the presentinvention. The decreased activation energy necessary when utilizing theactivated radicals results in a decrease in the deposition temperaturenecessary for the CVD process. As discussed above, a lower depositiontemperature is desirable for integrated circuit fabrication oftemperature-sensitive circuits requiring deposition temperatures below650° C.

The deposition rate of tungsten was also plotted as a function of thesusceptor rotation rate or substrate rotation rate. FIG. 5 illustratesthat the deposition rate for the thermal process increased withincreasing rotation rate as expected. This is due to the fact that themolecular reactants are being pumped to the rotating substrate surfaceat a higher rate. However, for the upstream radical-assisted process ofthe present invention, the deposition rate increased much moredramatically as the rotation rate increased. That is, there is an effectbeyond the basic pumping of reactants caused by the rotating substratewhich produces the increased deposition rate. With the upstream plasmamethod of the present invention, it was determined that the laminar gasflow pattern provided by the rotating susceptor minimizes the gas phasecollisions, and thus reduces the rate at which the necessary activatedhydrogen radicals H* recombine to form hydrogen molecules H₂. Theefficient delivery of radicals to the substrate surface in the upstreammethod of the present invention is an important advancement inplasma-enhanced CVD. A majority of the activated radicals are carried tothe substrate surface to take place in the surface deposition reaction.Therefore, not only do the activated radicals contribute energy andlower the deposition temperature, but also the high density of radicalsdelivered to the substrate by the laminar gas flow of susceptor 20further reduces the deposition temperature below the impractically hightemperatures of thermal CVD techniques.

FIG. 1A shows an alternative CVD configuration which utilizes anupstream microwave source to generate activated gas radicals. A reactor100 includes a chamber housing 102 enclosing reaction space 104. Likereactor 5 of FIG. 1, the housing may be controllably vacuumed to adesired internal deposition pressure. Plasma gases are introduced into avertical quartz tube 106. A microwave wave guide structure 108 iscoupled to quartz tube 106. Wave guide structure 108 includes ahorizontal section 110 which includes a microwave source 112. An angledwaveguide section 114 connects horizontal section 110 to a verticalwaveguide section 116. Quartz tube 106 extends through an opening (notshown) in the angled section 114 and extends through section 114 andvertical section 116 whereupon it extends through a top cover plate 15of housing 102. Quartz tube 106 extends through plate 118 and terminatesat an outlet end 120 above a gas dispersing showerhead 122. Showerhead122 is attached to a quartz insulator ring 124 which connects theshowerhead 122 to the cover 115 of reactor housing 102. Also disposedabove showerhead 122 and adjacent the outlet end 120 of quartz tube 106is a reactant gas halo or dispersion ring 128 which has a plurality ofopenings for dispersing reactant gas. A source line 130 is connected toring 128 for delivering a reactant gas such as TiCl₄ to the ring 128.

The microwave source 112 within wave guide section 110 may be amagnetron or any other suitable source which generates energy atmicrowave frequencies. For example, a coaxial waveguide adapter (notshown) might be attached onto one end of horizontal waveguide section110 to generate the necessary microwave energy.

The upstream microwave plasma source and reactor 100 of FIG. 1A operatessomewhat similarly to reactor 5 in FIG. 1. That is, a plasma gas such ashydrogen, nitrogen and/or ammonia is introduced into quartz tube 106 andtravels along the quartz tube 106 and through the microwave waveguidestructure 108 such that the gases are excited into a plasma within asection or area of tube 106. A rotating susceptor 132 supports asubstrate 134 below showerhead 122 and halo 128. Similar to the rotatingsusceptor of FIG. 1, susceptor 132 is coupled to a temperature controldevice (not shown) which heats substrate 134 to a desired temperature.Furthermore, susceptor 132 is coupled by shaft 134 to a motor (notshown) such that the rotation of susceptor 132 may be set as desired.The rotating susceptor pumps the activated radicals from end 120 ofquartz tube 106 and from reactant gas from ring 128 through showerhead122 to react and deposit a film layer onto substrate 134. Preferably,the majority of activated plasma particles reaching substrate 134 areactivated radicals which contribute energy to the surface reaction toachieve low temperature CVD. The remaining non-utilized gases areexhausted through an exhaust port 138.

While the laminar gas flow of a rotating susceptor in combination withan upstream plasma source yields desirable radical densities, a methodof low temperature CVD of titanium has also been achieved using a gasdispersing showerhead biased as an RF electrode in order to generate aplasma of ions and radicals close to the substrate such that both ionsand radicals contribute to the low temperature surface reactions.Accordingly, FIG. 2 shows a preferred embodiment of a CVD reactor forachieving low temperature deposition using activated radicals and ionsin accordance with the principles of the present invention. Referring toFIG. 2, the reactor 40 includes a deposition chamber housing 42 andhousing cover 43 which defines a reaction space 44. Housing 42 alsoencloses a rotating susceptor 46 which supports a substrate 48 in space44. Similar to the reactor of FIG. 1, reactor 40 may be selectivelyevacuated to various different internal pressures, while susceptor 46 iscoupled to adjustable heat and rotational controls for heating androtating substrate 48 at various temperatures and speeds, respectively.

Extending downwardly from the top of housing 42 is a cylinder assembly50 which is attached to a showerhead 52. Showerhead 52 is suspendedabove substrate 48. The gases to be excited into a plasma are introducedthrough a gas injection ring 54 into cylinder assembly 50 through aplurality of ring holes 56. Ring 54 is connected to a plasma gas supplyby line 55. Showerhead 52 is coupled to an RF power source 57 byfeedline assembly 58 which extends through cylinder assembly 50 toshowerhead 52. Cylinder assembly includes a cylinder 51, and insulatorring 60 which separates cylinder 51 and showerhead 52 for reasonsdiscussed hereinbelow. In one embodiment of the reactor 40, cylinder 51is electrically grounded. The RF energy biases showerhead/electrode 52so that it acts as an electrode and has an associated RF field.Showerhead/electrode 52 is preferably approximately 0.25 inches thickand contains approximately 300-600 dispersion holes 62. The gasesintroduced through plasma gas injection ring 54 flow downwardly incylinder 51. The RF field created by the biased showerhead/electrode 52excites the gases so that a plasma is created below the lower surface 53of showerhead/electrode 52. Preferably, the showerhead dispersion holes62 are dimensioned somewhat smaller than the gas dispersion holes oftraditional gas showerheads to prevent creation of a plasma in the holes62 which results in deposition in the holes and subsequent bombardmentof the substrate 48. Furthermore, the smaller holes 62 of the showerhead52 prevent formation of a plasma above showerhead 52 inside of cylinder51 thus concentrating the plasma below showerhead/electrode 52 and closeto substrate 48. The showerhead holes 62, in a preferred embodiment, aredimensioned to be approximately 1/32 of an inch wide. Cylinder 51preferably has the same diameter as showerhead/electrode 52 to spreadthe plasma and reactant gases over the entire showerhead 52.

The reactant gases, such as TiCl₄ are introduced through a ring 66 whichis generally concentric with ring 54 and is connected to a reactant gassource by line 64. The gas flow from injector rings 54 and 66 developswithin the length of the cylinder 51 as the gases travel to theshowerhead/electrode 52. Utilizing the rotating susceptor 46, thecylinder 51, and showerhead/electrode 52, it is preferable for thevelocity profile of the incoming plasma gases passing through showerhead52 to be fully developed before it reaches the rotating substrate 48.The showerhead/electrode 52 is spaced between 0.25 to 4 inches from thesubstrate 48 to ensure that the plasma is close to the substrate 48.Preferably, the spacing is under 1 inch and in a preferred embodiment isapproximately 20 millimeters. As the gases pass through theshowerhead/electrode 52, the pressure drop across theshowerhead/electrode 52 flattens out the velocity profile of the gases.That is, the gas tends to have the same velocity at the center of theshowerhead/electrode 52 as around the periphery. This is desirable foruniform deposition of a film on substrate surface 49. The plasma gasespass through showerhead/electrode 52 and are excited into a plasmaproximate the bottom side 53 of showerhead/electrode 52. As mentionedabove, it has been found that an RF plasma may be excited with RF energyas low as 450 KHz and as high as 13.56 MHZ and the invention does notseem to be particularly frequency sensitive.

If susceptor 46 is rotated with the deposition configuration of FIG. 2,the pumping effect of the rotating susceptor 46 takes place below theshowerhead/electrode 52. In the embodiment of the present invention asshown in FIG. 2, the unique use of showerhead/electrode 52 in very closeproximity to substrate 48 produces a concentrated plasma with a largedensity of useful gas radicals and ions proximate the substrate surface49. With the RF showerhead/electrode configuration of FIG. 2, it hasbeen discovered that there does not seem to be a noticeable enhancementgained in rotating the susceptor 46 faster than approximately 100 rpm.It was also found, however, that a rotation rate of 0 rpm, although notdrastically affecting the deposition rate, lowers the uniformity of thereactant and plasma gas flow and the subsequent deposition. Generally, asubstrate rotation rate between 0 and 2,000 rpm might be utilized withthe deposition configuration utilizing an RF showerhead/electrode.

As illustrated further hereinbelow, a susceptor rotation rate ofapproximately 100 rpm has proven to be sufficient for deposition. Whileit is preferable to utilize only radicals in the upstream plasmageneration methods, both radicals and ions are present during thedeposition using RF showerhead/electrode 52. That is, both ions andradicals supply energy to the surface reaction. While it is generallynot desirable to use only ions due to their tendency to stick to contactand via surfaces and produce non-conformal films, some ion bombardmentof the substrate 48 is beneficial because it supplies additional energyto the growing film layer on the surface 49 of the substrate 48.However, too much ion bombardment of substrate 48 may damage theintegrated circuit devices of the substrate 48 and may lead to poor filmconformality. Therefore, the deposition parameters and showerheadspacing are chosen as illustrated herein to achieve a useful mixture ofradicals and ions. As discussed above, for the configuration of FIG. 2,the spacing is under 1 inch and preferably approximately 20 mm.

The reactant gases, such as TiCl₄, are introduced into cylinder 51through another gas ring 66. The reactant gases travel down the lengthof cylinder 51 and are also excited by the RF field created byshowerhead/electrode 52, as they pass through the openings 62 ofshowerhead 52. The reactant gas travels to the surface of substrate 48along with the radicals and ions of the excited plasma. The radicals,ions and excited reactant gas particles react at the surface ofsubstrate 48 to deposit a film such as a titanium-containing film, uponsubstrate 48.

Because of the close spacing of the showerhead/electrode 52 fromsubstrate 48 in combination with cylinder 51, the gas mixturestreamlines 65 emanating from showerhead 52 are close to the substrate48 to provide efficient deposition and reduce the amount of gas mixturewhich bypasses the substrate 48. That is, the boundary layer of gas,which is defined as the volume or space below the gas streamlines 65which is stagnant or non-moving with respect to the susceptor 46, isvery small. Therefore, a large percentage of the radicals, ions andreactant gas particles are being utilized in the surface reaction, andaccordingly, the efficiency of the CVD process and the deposition rateare increased.

With the showerhead/electrode 52 acting as an RF electrode, a moreuniform plasma is generated at substrate 48, therefore enhancing theuniformity of radical and ion density at the substrate 48 and theuniformity of the deposited film. In the RF showerhead/electrodeconfigurations of FIGS. 2, 2A and 2B the deposition rate reaches amaximum when the rotation rate is matched to the incoming plasma andreactant gas flow, i.e., matched gas flow. Accordingly, it is desirableto achieve matched flow when susceptor 46 rotates.

FIG. 2A discloses an RF showerhead/electrode configuration similar tothe configuration of FIG. 2 except in greater detail. Wherever possiblesimilar reference numerals will be utilized between FIGS. 2 and 2A. Theconfiguration of FIG. 2A is similar to a structure disclosed within U.S.patent application Ser. No. 08/166,745, now U.S. Pat. No. 5,647,911, thedisclosure of which is fully incorporated herein by reference.

In FIG. 2A, there is shown in break-away a portion of CVD depositionchamber housing 42, to which is mounted the RF showerhead/electrodeapparatus 142 used to practice the low temperature deposition of thepresent invention. It will be appreciated by persons skilled in the artthat certain features to be described may pertain to one or more, butless than all, embodiments of the invention. In FIG. 2A, theshowerhead/electrode 52 includes an RF line stem 144 mounted thereto. Aswill be discussed in further detail, the RF line stem 144 is one ofseveral components making up the RF feedline assembly 58. The RFfeedline assembly 58 also acts as a heat pipe to conduct heat away fromshowerhead/electrode 52 as is also discussed further hereinbelow.Preferably, line stem 144 is machined concentrically into and isintegral with upper surface 146 of showerhead/electrode 52 to increasethe RF signal conduction and heat conduction efficiency. RF line 148comprises line stem 144 and an additional length of tubing 150 weldedthereto to achieve the desired overall length of the RF line 148. Theweld is represented at 149. Preferably, showerhead/electrode 52 andintegral line stem 144 are made of Nickel-200, while RF line tubing 150is made of a highly conductive material such as 6061-T6 aluminum.However, it will be appreciated by persons skilled in the art that othermaterials can be used for the RF line 150, such as nickel 200. In oneembodiment, the RF line 148 is made of aluminum coated with nickel toprevent an RF plasma from forming within said cylinder 51 of thecylinder assembly 50 during the plasma-enhanced CVD reactions of thepresent invention. Preferably, the showerhead/electrode is approximately0.25 inches thick.

Showerhead/electrode 52 is perforated with a pattern of gas dispersionholes 62 to distribute the reactant and plasma gases evenly during CVDprocessing. As shown in FIG. 2A, upstanding RF line stem 144 is providedwith a circumferential shoulder flange 152 adjacent and parallel toshowerhead/electrode 52. The flange 152 is spaced aboveshowerhead/electrode upper surface 146 and permits the gas dispersionhole pattern to extend beneath the shoulder flange 152, therebyminimizing gas flow disturbances. Furthermore, the flange 152 aids inthe conduction of the RF energy along line 148 to showerhead/electrode52, assists in cooling showerhead/electrode 52, and provides mechanicalsupport for ceramic isolator tubes 154, 156. An alternative embodimentof the showerhead electrode configuration eliminates the flange 152 asshown in FIG. 2B.

The RF showerhead/electrode apparatus 142 of FIG. 2A further includesfirst and second ceramic isolator tubes 154, 156, respectively, whichare concentric with and surround at least a portion of RF line 148. Asshown, ceramic isolator tubes 154, 156 are supported by circumferentialshould er flange 152. Tubes 154, 156 are preferably formed of alumina(99.7% Al₂ O₃) which is readily commercially available such as fromCoors Ceramics of Golden, Colo. One function of these isolator tubes154, 156 is to prevent RF plasma from forming around the RF line 148during CVD processing by isolating the RF line 148 from the plasma andreactant gases in the cylinder assembly 50. As may be appreciated, it isdesirable to prevent the formation of any plasma within the cylinderassembly 50 in order to concentrate the plasma belowshowerhead/electrode 52. Therefore, the isolator tubes 154, 156 operateto prevent the formation of such a plasma inside of the cylinderassembly 50. Additionally, and as described more fully below, theisolator tubes 154, 156 aid in preventing electrical shorting betweengas distributor cover 158 (which is at ground potential) and RF line 148at the location where RF line 148 passes through gas distributor cover158. Gas distributor cover 158 is mounted to housing 42 by means of aplurality of screws 150. As shown in the FIG. 2A, gas injection rings orhalos such as rings 54, 66 (shown in phantom) are located slightly belowgas distributor cover 158 and supply the CVD reaction and plasma gasesto the inside of cylinder assembly 50. Gas injection rings 54, 66 may betwo of a plurality of concentric rings for introducing numerous reactantgases.

A seal prevents vacuum leaks at the location where RF line 148 passesthrough gas distributor cover 158. This is accomplished by means of ashaft seal and a flange seal. As shown in the FIG. 2A, a ceramic sealplate 160 is pressed downwardly by two stainless steel clamps 162.Clamps 162 are biased against distributor cover 158 by springwasher/screw assemblies 164 to obtain a predetermined downward force onthe seal components to insure proper sealing, to accommodate tolerancestacks in the seal components, and to take up dimensional changes due tothermal expansion which may occur during CVD processing. Seal plate 160presses downwardly on a stainless steel ferrule 166 which in turnpresses down on an O-ring 168 seated in ceramic seal body 170. Thedownward force exerted by clamps 162 on seal plate 160 also forces sealbody 170 downwardly against gas distributor cover 158, which compressesthe O-ring 172 located between seal body 170 and gas distributor cover158. It should be noted that seal body 170 has a downwardly extendingannular flange 174 which surrounds RF line 148 over the entire length ofit which passes through gas distributor cover 158. The lower end 176 ofannular flange 174 extends downwardly to a point where it meets ceramicisolator tube 154. As shown, the outer ceramic isolator tube 156 extendsfurther upward than isolator tube 154, such that there is no direct linebetween gas distributor cover 158 and RF line 148. This prevents arcingwhen the RF line 148 is used to power showerhead/electrode 52.

The RF line 148 also functions as a heat pipe structure. With respect toheat pipe structures, such devices are known per se, and in the presentinvention, the heat pipe structure is used to carry off heat from theshowerhead/electrode 52 generated by radiant energy from the heatedsusceptor 46, as well as by the RF energy applied to theshowerhead/electrode. The center space 178 of RF line 148 is providedwith a felt or other suitable capillary wicking material liner (notshown). Space 178 is sealed with a liquid (e.g., acetone) therein underits own vapor pressure that enters the pores of the capillary materialwetting all internal surfaces of RF line 148. By applying heat at anypoint along the length of the RF line, the liquid at that point boilsand enters a vapor state. When that happens, the liquid in the wickingmaterial picks up the latent heat of vaporization and the vapor, whichthen is at a higher pressure, moves inside the sealed pipe to a coolerlocation where it condenses and re-enters the liner. Thus, the vaporgives up its latent heat of vaporization and moves heat from the "input"to the "output" end of the heat pipe structure. As a general frame ofreference, heat may be moved along a heat pipe at a rate ofapproximately 500 mph.

With reference to the specific configuration utilized in FIG. 2A, the"input" end of the heat pipe structure is the end which is affixed toshowerhead/electrode 52. The "output" end is the upper end shown in theFIG. 2A which has a liquid-cooling jacket 180 sealed around it. The sealis effected by O-ring shaft seals 182 and 183. Cooling jacket 180 ispreferably a polymeric material and is provided with TEFLON compressionfittings 184 and 185 which connect TEFLON tubing 186 to cooling jacket180. A suitable cooling liquid, such as water, flows through tubing 186and cooling jacket 180 to carry heat away from RF line 148. This permitsdirect contact of the cooling liquid with the RF line 148 for efficientconduction of heat from the line 148. Additionally, with thisconfiguration, at no time is the CVD reactor chamber exposed to thepossibility of an internal coolant leak, nor is there any corrosiveeffect on metal tubing by RF carrying liquid. As stated, the fluid whichpasses through TEFLON tubing 186 and carries the heat away from the RFline 148 may be water, although a variety of fluids can be useddepending on the heat to be conducted away from the line 148. RF line148 also includes a cap 188 which is welded in place and has a fill tube190 for filling the internal space 178 with the desired fluid. Asuitable commercially available heat pipe may be obtained fromThermocore Inc., of Lancaster, Pa.

As shown in FIG. 2A, an aluminum cylinder 51 is utilized to vary theshowerhead/electrode substrate spacing(s). Showerhead/electrode 52 isfastened to cylinder 51 by means of screws 192, which are preferablymade of a material that does not corrode in the presence of an RFplasma. One such material is Hastelloy C-22, which is a trade name ofHanes International, of Kokomo, Ind. Suitable screws made of thismaterial are available from Pinnacle Mfg. of Tempe, Ariz. Quartz ring 60electrically isolates showerhead/electrode 52 from aluminum cylinder 51.A suitable quality quartz for ring 60 is Quartz T08-E available fromHereaus Amersil in Tempe, Ariz. Screws 192, which are at groundpotential, are isolated from the showerhead/electrode 52 by twointerlocking ceramic isolator sleeves 194 and 196. Quartz is used forisolator ring 60 because of its significant resistance to thermal shock.This can be important since the RF showerhead/electrode 52 below quartzring 60 becomes heated to a higher temperature, and more rapidly thanaluminum cylinder 51 above quartz ring 60, thus inducing thermal shockand stress in ring 60. Screws 198, which may be made of the samematerial as screws 192, are utilized to affix aluminum cylinder 51 tohousing 42. As discussed above, various length cylinders 51 might beutilized to vary the showerhead/electrode-to-substrate spacing. It ispreferable that the length of cylinder 51 be chosen to positionshowerhead/electrode 52 within 1 inch of susceptor 46.

RF energy is conducted to showerhead/electrode 52 by RF feedlineassembly 58 comprising stem 144 and tube 150. Isolator tubes 154, 156are needed to electrically isolate and prevent arcing between tubing 150and any parts of the metal housing 42, including distributor cover 158.Furthermore, the apparatus includes a seal around tubing 150 at thelocation where it passes through distributor cover 158, as describedhereinabove and shown in FIG. 2A.

RF energy is supplied through a shielded RF supplying cable 200 which isconnected to an RF power source 57 (not shown in FIG. 2A) and has a UHFconnector 202 at one end. Connector 202 mates with another UHF connector204, which in turn is coupled via a length of 12 gauge wire 206 to astainless steel shaft collar 208 mounted at the upper end of RF line148. With this arrangement there is minimal resistance to the flow of RFcurrent. The segment of RF line 148 which is exposed above shaft collar208 is isolated from the grounded metal shielding 210 by a polymer cap212. The apparatus is believed to be capable of delivering 250-300 wattsof RF power at 450 KHz to 13.56 MHZ.

FIG. 2B shows an alternative embodiment of the RF showerhead/electrodeconfiguration utilized to practice the present invention. The CVDapparatus 220 of FIG. 2B operates similarly to the apparatuses shown inFIGS. 2 and 2A. That is, an RF showerhead/electrode 222 is biased by anRF feedline assembly 224 while plasma and reactant gases are pumpedthrough a cylinder assembly 226 to a substrate 228 on susceptor 230.However, the embodiment of FIG. 2B eliminates the metal cylinder 51 andinsulator ring 60 of FIGS. 2 and 2A while preventing electrical arcinginside of the cylinder assembly 226 proximate the RF line and preventingthe undesired formation of plasma within the cylinder assembly 226 whenthe showerhead 222 is biased as an electrode. The embodiment of FIG. 2Butilizes a housing, such as one similar to housing 42 of FIG. 2, whichincludes a housing cover 232 and includes an RF supply assembly 234, aheat pipe assembly 236 with cooling jacket 237 and associated fluidsupply lines and a gas distributor cover 239 with a sealing assembly 241all generally similar to the respective components of FIG. 2. However,the cylinder assembly 226 does not include a metal cylinder 51 andinsulator ring 60 as shown in FIG. 2. Rather, a cylinder 238 made of aninsulating material such as quartz surrounds the RF feed line assembly224.

Cylinder 238 is preferably formulated out of a high quality quartz suchas Quartz T08-E available from Hereaus Amersil, as mentioned above.Quartz cylinder 238 is supported by a nickel showerhead/electrode 222,made of a conductive metal such as Nickel-200, without the use of screwsor other fasteners that are utilized within the embodiments of FIGS. 2and 2A. Specifically, a stepped bore 240 is formed within housing cover232 to receive an upper end 242 of cylinder 238. O-rings 243, 244 areplaced at the interface between stepped bore 240 and cylinder 238 toform a seal at the interface. At the lower end 246 of cylinder 238, anannular notch 248 is formed in cylinder 238 to receive a peripheral edge250 of the showerhead/electrode 222. The notch 248 of cylinder 238 restsupon the peripheral edge 250 of showerhead/electrode 222.Showerhead/electrode 222 includes a stem 252 which is attached to RFline tubing 254, such as by a weld at 255, to form a unitary RF line256. RF line 256 is frictionally held and supported at its top end bycollar 258 similar to collar 208 of FIG. 2A. The RF line, in turn,supports showerhead/electrode 222 above susceptor 230.Showerhead/electrode 222, in turn, supports the cylinder 238 within thecylinder assembly 226 by abutting against cylinder 238 at notch 248 andholding it in bore 240. The interface between showerhead/electrodeperipheral edge 250 and cylinder notch 248 is sealed by a compressedO-ring 258 which is compressed between shelf 248 and a similarcorresponding annular notch 260 formed in peripheral edge 250 of theshowerhead/electrode 222. Similar to the embodiments of FIGS. 2 and 2A,a plurality of gas halos or rings 262, 264 introduce the necessaryplasma and reactant gases into cylinder 238.

The embodiment of FIG. 2B eliminates the need for metal screws to attachthe cylinder 238 to the housing cover 232 and the showerhead/electrode222 to the cylinder 238. This further reduces the possibility of arcinginside of cylinder 238 because of the reduced metal proximate the biasedRF showerhead/electrode 222. Furthermore, it is not necessary to utilizeceramic isolator sleeves at the showerhead peripheral edge 250.

Accordingly, the RF showerhead/electrode 222 has also been modified.Showerhead/electrode 222 includes a stem 252 without a flange. Instead,a slight ridge 266 is formed around stem 252, and as shown in FIG. 2A,ridge 266 supports a generally circular ceramic tray 268 which is formedfrom a ceramic material, such as alumina (99.7% Al₂ O₃), similar to theceramic isolator sleeves 154, 156 shown in FIG. 2A. Ceramic tray 268 issupported by ridge 266, and in turn, supports isolator sleeves 270, 271.Isolator sleeves 270, 271 are also preferably made of a ceramicinsulator material similar to that used for sleeves 154, 156 of FIG. 2A.As with the embodiments used to practice the present invention which arediscussed above, preferably the holes of showerhead/electrode 22 areapproximately 1/32 (0.0313) inches in diameter to prevent the formationof a plasma inside cylinder 238 and to confine the plasma generallybelow the showerhead/electrode 222 and above the susceptor 230. Theembodiment of FIG. 2B utilizes quartz cylinder 238 and eliminates themetal attachment screws proximate showerhead/electrode 222 which helpsto prevent the formation of a plasma within cylinder 238 and to preventarcing between the RF line 256 and showerhead/electrode 222 and any ofthe surrounding metal. A layer of insulation 272 may be placed atop gasdistributor cover 239 to prevent contact by an operator, because the gasdistributor cover 239 becomes very hot during operation.

Numerous deposition runs have been made utilizing the RFelectrode/showerhead configuration of FIGS. 2 and 2A to illustrate theviability of the present invention. Specifically, a layer of titaniumnitride was deposited upon a substrate wafer at approximately atemperature of 400° C. This is substantially lower than the substratetemperature which is ordinarily required for thermal CVD processes totake place, which may be well over 1,000° C. For example, a layer oftitanium nitride was deposited using ammonia gas (NH₃) and nitrogen gas(N₂) with the parameters listed below and the results shown in Table 1.The configuration of the present invention utilizes plasma gas flowsbetween 500 and 5,000 sccm (50 to 500 sccm for NH₃) while a reactant gasflow, such as TiCl₄, between 0.5 and 10 sccm is desired. The reactionspace 44 should be evacuated between 0.5 to 10 Torr.

Deposition Parameters for Table No. 1

TiCl₄ (sccm) 10

NH₃ (sccm) 500

N₂ (sccm) 500

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 1

Susceptor Rotation Rate (rpm) 100

Substrate Temp. (°C.)

                  TABLE NO. 1    ______________________________________    Results and Additional                   WAFER NO.    Deposition Parameters                   1      2      3    4    5    6    ______________________________________    TiN layer thickness (Å)                   800    698    608  545  723  910    Deposition Rate (Å/min)                   400    348    304  272  241  303    Layer Resistivity (μΩ-cm)                   1519   1194   970  940  1021 1284    Deposition Time (sec).                   120    120    120  120  180  180    Susceptor Temp (°C.)                   414    471    457  461  462  475    ______________________________________

Wafers 1-3 were silicon, while wafers 4-6 were thermal oxide wafershaving a thin layer of silicon dioxide on the surface. This was done toensure that the process of the present invention may be utilized in abroad range of CVD applications for both silicon wafers and oxidewafers. Each of the substrate wafers of Table 1 were also given an RFplasma ammonia (NH₃) anneal in the apparatus of FIG. 2 at 250 Watts forapproximately 120 seconds with a gas concentration of 5,000 sccm of NH₃at a pressure of 5 Torr. The rotation rate of the susceptor during theanneal was approximately 100 rpm. The NH₃ RF plasma improves the filmquality of the deposited TiN film as discussed further hereinbelow.

The RF plasma electrode/showerhead configuration, in accordance with theprinciples of the present invention, may be utilized to deposit atitanium nitride (TiN) layer on a substrate utilizing both nitrogen gas(N₂) and hydrogen gas (H₂) instead of ammonia gas (NH₃). The variousfilm results and deposition parameters for the H₂ and N₂ low temperaturedeposition of TiN are given below in Table Nos. 2, 3, 4 and 5, atincreasing deposition temperatures for increasing table numbers.

Deposition Parameters for Table No. 2

TiCl₄ (sccm) 10

H₂ (sccm) 500

N₂ (sccm) 500

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 1

Susceptor Rotation Rate (rpm) 100

Substrate Temp. (°C.) 400

Deposition Time (seconds)

                                      TABLE NO. 2    __________________________________________________________________________    Results and    Additional          WAFER NO.    Parameters          1  2   3  4   5  6  7   8  9  10    __________________________________________________________________________    TiN layer          825             1023                 1221                    1262                        1227                           1224                              1141                                  1348                                     1400                                        1106    thickness    (Å)    Deposition          275             341 407                    421 409                           408                              380 449                                     487                                        389    Rate    (Å/min)    Layer 1530             26864                 4118                    3108                        855                           4478                              3982                                  4658                                     3449                                        4501    Resistivity    (μΩ-cm)    Susceptor          470             480 488                    470 470                           460                              460 460                                     460                                        460    Temp (°C.)    __________________________________________________________________________

Wafers 1 and 2 of Table No. 2 were silicon, while the remaining wafers3-10 were thermal oxide. Wafers 6-10 received a 250 Watt RF plasmaanneal for 120 seconds at an NH₃ gas rate of 5,000 sccm, at an internalpressure of 3 Torr (wafer 6 was done at 5 Torr), and a susceptorrotation rate of 100 rpm.

Table No. 3 illustrates the results of deposition runs utilizing asubstrate temperature of 450° C., but maintaining the same gas anddeposition parameters as were used in the deposition runs of Table No.2. Wafer 1 and 2 were silicon while wafers 3-8 were thermal oxide. Theresults are as follows with wafers 6-8 of Table No. 3 receiving a 120second RF plasma ammonia anneal at 5000 sccm, 5 Torr and a 100 rpmrotation rate with a power level of 250 Watts.

                  TABLE NO. 3    ______________________________________    Results and    Additional             WAFER NO.    Parameters             1      2      3    4    5    6    7    8    ______________________________________    TiN layer             996    1009   1064 1488 1562 1444 1381 1306    thickness    (Å)    Deposition             332    336    355  496  521  481  454  435    Rate    (Å/min)    Layer    640    607    666  815  821  7121 5812 6363    Resistivity    (μΩ-cm)    Susceptor             518    519    521  524  521  522  524  523    Temp (°C.)    ______________________________________

The low temperature TiN deposition was repeated with the substratetemperature at 500° C. and the results are tabulated according to TableNo. 4 below. Wafer 1 was silicon and wafers 2-7 were thermal oxide.

                  TABLE NO. 4    ______________________________________    Results and    Additional            WAFER NO.    Parameters            1       2      3     4    5     6    7    ______________________________________    TiN layer            990     1086   1034  1092 1004  1001 1004    thickness    (Å)    Deposition            330     362    345   364  335   334  335    Rate    (Å/min)    Layer   578     687    700   786  1892  1840 1886    Resistivity    (μΩ-cm)    Susceptor            579     590    597   595  591   593  594    Temp (°C.)    ______________________________________

Wafers 1-4 in Table No. 4 were not annealed, while wafers 5-7 wereannealed using a similar RF plasma NH₃ anneal process and the parametersused for the deposition runs referenced in Table No. 3.

Similarly with a substrate temperature of 600° C., the CVD process ofthe present invention was used to deposit TiN with the results shown inTable No. 5 below, with wafers 1 and 2 being silicon and wafers 3-8being thermal oxide.

                  TABLE NO. 5    ______________________________________    Results and    Additional             WAFER NO.    Parameters             1      2      3    4    5    6    7    8    ______________________________________    TiN layer             657    822    740  768  767  765  773  910    thickness    (Å)    Deposition             219    274    247  263  256  255  258  303    Rate    (Å/min)    Layer    391    254    432  543  471  949  973  2710    Resistivity    (μΩ-cm)    Susceptor             650    650    650  650  650  650  650  656    Temp (°C.)    ______________________________________

Again, an RF plasma NH₃ anneal was performed on substrate wafers 6-8 ofTable No. 5 similar to the anneal step of tables 3 and 4 except at apressure of 1 Torr instead of 5 Torr. Therefore, the deposition of TiNusing the low temperature CVD process of the present invention may beaccomplished at various temperatures lower than the temperaturesnecessary for traditional thermal CVD.

While titanium nitride may be deposited with the present invention, itmay also be desirable to deposit simply a layer of pure titanium. Forexample, a titanium layer might be deposited upon a silicon wafer whichthen reacts with the titanium to form a film of titanium silicide(TiSi₂). To this end, the present invention may also be used to depositlayer of titanium.

Table No. 6 below sets forth the results and parameters of a depositionrun which resulted in a deposited film of approximately 84% titanium ona thermal oxide wafe at 650° C. This was an excellent result for suchlow temperature chemical vapor deposition. The deposition run of Table 6was performed according to the following deposition parameters, with theRF showerhead/electrode configuration of FIG. 2.

Deposition Parameters for Table No. 6

TiCl₄ (sccm) 10

H₂ (sccm) 500

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 1

Susceptor Rotation Rate (rpm) 100

Deposition time (sec) 2700

Substrate Temperature (°C.)

                  TABLE NO. 6    ______________________________________    WAFER NO.            Results and            Additional            Parameters                    1    ______________________________________            Ti layer                    1983            thickness            (Å)            Deposition                    44            Rate            (Å/min)            Layer   929            Resistivity            (μΩ -cm)            Susceptor                    651            Temp (°C.)    ______________________________________

The substrate wafer of Table No. 6 was not annealed.

Additional Ti-layer deposition runs were made according to the Table No.7 parameters below with the following results shown in Table No. 7:

Deposition Parameters for Table No. 7

TiCl₄ (sccm) 10

H₂ (sccm) 500

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 0.85

Susceptor Rotation Rate (rpm) 100

Deposition time (sec) 120 (wafer 7 for 180 sec)

Substrate Temperature (°C.) 565

Susceptor Temperature (°C.)

                                      TABLE NO. 7    __________________________________________________________________________    Results and    Additional          WAFER NO.    Parameters          1   2   3  4  5   6   7   8  9  10 11 12    __________________________________________________________________________    Ti layer          134.8              466.2                  209.2                     100.8                        194.04                            154.98                                115.92                                    114.7                                       152.5                                          39.06                                             41.6                                                50.4    thickness    (Å)    Deposition          67.4              233.1                  104.6                     50.4                        97.0                            77.5                                38.6                                    57.3                                       76.2                                          19.5                                             20.6                                                25.2    Rate    (Å/min)    Layer 2116.1              1767.8                  761.8                     -- --  --  1001.4                                    371.6                                       321.6                                          -- -- --    Resistivity    (μΩ-cm)    __________________________________________________________________________

Wafers 1-3 and 7-9 of Table 7 were silicon while the remaining waferswere thermal oxide. None of the wafers of Table No. 7 received an RFplasma anneal of NH₃.

Since a benefit of chemical vapor deposition of titanium-containingfilms is improved step coverage and film conformality over the physicaldeposition techniques, several of the film layers deposited according tothe present invention were tested to measure conformality and stepcoverage. The layers tested for conformality and step coverage weredeposited according to the parameters of Table No. 8 with the resultsshown in Table No. 8 below. The film conformality and step coverage ofthe film layers deposited according to the parameters below were verygood.

Deposition Parameters for Conformality and Step Coverage Deposition Runsof Table 8

TiCl (sccm) 10

H₂ (sccm) 500

N₂ (sccm) 500

RF Power (watts) 250 @ 450 KHz

Reactor Chamber Pressure (Torr) 1

Susceptor Rotation rate (rpm) 100

Substrate Temperature (°C.) 450

Susceptor Temperature (°C.)

                  TABLE NO. 8    ______________________________________    WAFER NO.    Results and    Additional    Parameters        1      2    ______________________________________    TiN layer         586    2423    thickness    (Å)    Deposition        362    304    Rate    (Å/min)    Layer             --     --    Resistivity    (μΩ -cm)    Susceptor         520    520    Temp (°C.)    ______________________________________

None of the wafers used in Table 8 and tested for step coverage wereannealed with an RF plasma of NH₃.

As illustrated above a layer of titanium nitride (TiN) may be depositedin accordance with the principles of the present invention withoututilizing ammonia gas (NH₃). Instead, a mixture of H₂ and N₂ gases isused. Low temperature deposition of titanium nitride using TiCl₄, N₂,and H₂ is desirable because it reduces contaminants within the reactionchamber that are formed by the chemical reactions of TiCl₄ and NH₃. Morespecifically, TiCl₄ reacts with NH₃ at temperatures below 120° C. toform a yellow powdery adduct, and to prevent the adduct from forming itwas necessary in the past to heat the reaction chamber walls to at least150° C. Since it is now possible to deposit a layer of titanium nitrideat low temperatures using TiCl₄, N₂, and H₂ chemistry instead of NH₃, itis no longer necessary to remove a deposited adduct or to heat thereaction chamber walls, thus greatly reducing the cost of CVD systems.

According to the deposition parameters of Table No. 9, a layer oftitanium nitride was deposited upon several thermal oxide substratesusing a reaction chamber with unheated walls and a gas mixture of H₂/N₂. After the deposition of the films, the reaction chamber wasinspected and there was no evidence of a yellow adduct found. None ofthe wafers of Table No. 9 were annealed with an RF NH₃ anneal.

Parameters for Adduct Test of Table No. 9

TiCl₄ (sccm) 10

N₂ (sccm) 500

H₂ (sccm) 500

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 1

Susceptor Rotation rate (rpm) 100

Substrate Temp. (°C.) 450

Deposition time (sec) 95

Susceptor Temperature (°C.) approximately

                                      TABLE NO. 9    __________________________________________________________________________    Results and    Additional          WAFER NO.    Parameters          1   2  3  4   5  6  7   8  9  10    __________________________________________________________________________    TiN layer          94  132                 127                    143 143                           160                              162 162                                     195                                        204    thickness    (Å)    Deposition          58  83 80 90  90 101                              102 102                                     123                                        129    Rate    (Å/min)    Layer 2164              2218                 1377                    660 764                           905                              738 830                                     689                                        702    Resistivity    (μΩ-cm)    Susceptor          525 523                 520                    520 520                           523                              521 520                                     519                                        523    Temp (°C.)    __________________________________________________________________________

Further deposition runs were made utilizing the configuration of FIG. 2wherein the plasma and reactant gas flows were adjusted, as well as theinternal deposition pressure of the reaction space 44. For example, thedeposition runs shown in FIG. 10 utilized a higher flow rate of H₂ andan increased deposition pressure from 1 Torr to 5 Torr. Further, Argonwas mixed with the H₂ for some of the deposition runs.

Parameters for Table 10

TiCl₄ (sccm) 10

H₂ (sccm) 5,000 (wafers 1-4); 3,750 (wafers 5-9)

Argon (slm) 0.5 (wafers 5-9)

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 5

Susceptor Rotation rate (rpm) 100

Deposition time (sec) 300 (600 for wafer 9)

Substrate Temp. (°C.) 565

Susceptor Temperature (°C.) approximately

                                      TABLE 10    __________________________________________________________________________    Results and    Additional          WAFER NO.    Parameters          1   2   3   4  5  6   7   8  9    __________________________________________________________________________    TiN layer          798 1076                  43.4                      89.5                         912.2                            1082                                656.5                                    577.1                                       1302    thickness    (Å)    Deposition          159.0              215.0                  9.1 17.9                         182.5                            216.5                                131.3                                    115.4                                       130.2    Rate    (Å/min)    Layer 53.84              32.66                  216.1                      377.1                         89.23                            25.7                                212.7                                    211.3                                       170.1    Resistivity    (μΩ-cm)    __________________________________________________________________________

In Table 10, the flow of H₂ was increased to 5,000 sccm for wafers 1-4and to 3,750 sccm for wafers 5-9. The deposition pressure was increasedto 5 Torr. For wafers 5-9, a flow of 0.5 standard liters per minute(slm) of Argon was utilized with the H₂ as a diluent. In Table 10,wafers 1-2 and 5-6 were silicon, while wafers 3-4 and 7-9 were thermaloxide.

Table 11 shows additional runs made with the increased H₂ flow andincreased deposition pressure.

Deposition Parameters for Table No. 11

TiCl₄ (sccm) 10

H₂ (sccm) 3,750

Argon (slm) 0.5

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 5

Susceptor Rotation Rate (rpm) 100

Deposition time (sec) 300 (wafers 9-12 600 seconds)

Substrate Temperature (°C.) 565

Susceptor Temperature (°C.)

                                      TABLE NO. 11    __________________________________________________________________________    Results and    Additional          WAFER NO.    Parameters          1   2   3  4  5  6  7  8  9  10 11 12    __________________________________________________________________________    TiN layer          889.6              3994                  510.3                     458.6                        466.2                           385.6                              347.8                                 263.3                                    792.5                                       948.8                                          749.7                                             714.4    thickness    (Å)    Deposition          177.9              79.9                  102.1                     91.7                        93.2                           77.1                              69.6                                 52.7                                    79.3                                       94.9                                          75.0                                             71.4    (Å/min)    Layer 54.03              35.71                  233.4                     274.1                        281.0                           280.1                              545.1                                 489.1                                    314.1                                       203.5                                          -- --    (μΩ-cm)    __________________________________________________________________________

The change in deposition pressure from 1 Torr to 5 Torr produced a morestable and symmetric plasma. Additionally, the increased hydrogen flowwith the addition of a small flow of argon increased the stability ofthe plasma flow as well as the plasma intensity. An argon flow of 0-10slm is preferable. Wafers 1-2 were silicon, while wafers 3-10 werethermal oxide. Wafers 11 and 12 were borophospho-silicate glass,available from Thin Films, Inc. of Freemont, Calif. None of the wafersof either Table 10 or 11 were annealed with a NH₃ plasma anneal.

Wafers 11 and 12 had field oxide (silicon oxide) top layers, patternedwith silicon contacts (i.e., vias through the field oxide to a lowersilicon layer). Selective deposition was observed in wafer number 11after processing in the manner described above. FIG. 6 shows depositionat the bottoms of silicon contacts (vias), but no deposition onto theoxide field. Selective deposition has been repeated and independentlyverified using the identified parameters. A selective deposition processcan be used in place of multiple process steps to form vias. Selectivedeposition may be a result of different nucleation times for silicon andsilicon oxide--nucleation occurs rapidly on silicon, but only afterapproximately 30 seconds on silicon oxide. Although the process appliedto wafer 11 ran for longer than the normal 30 second nucleation time ofsilicon oxide, nucleation apparently did not occur over silicon oxide,possibly due to an instability in the plasma. High process pressuresappear to be important for producing the selective effect.

Table 12 shows additional deposition runs at a susceptor temperature of450° C.

Deposition Parameters for Table No. 12

TiCl₄ (sccm) 5

H₂ (sccm) 3,750

Argon (slm) 0.3

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 5

Susceptor Rotation Rate (rpm) 100

Deposition time (sec) 180

Substrate Temperature (°C.) approximately 400° C.

Susceptor Temperature (°C.)

                  TABLE NO. 12    ______________________________________    Results and    Additional             WAFER NO.    Parameters             1      2       3    4     5    6     7    ______________________________________    TiN layer             242    222     210  241   168  136   150    thickness    (Å)    Deposition             80.7   74.0    70.0 80.3  56.0 45.3  50.0    Rate    (Å/min)    Layer    66.0   554.0   494.0                                 714.0 484.0                                            0.1   0.1    Resistivity    (μΩ-cm)    ______________________________________

Wafers 1-4 were silicon, wafer 5 was thermal oxide while wafers 6 and 7were an aluminum alloy containing aluminum silicon and copper. Runs 6and 7 of Table 12 illustrate the viability of depositing atitanium-containing film on aluminum using the present invention. Thedeposition runs of Table 12 utilized a lower flow of reactant gas thanthe runs of Table 11, i.e., 5 sccm of TiCl₄.

Good adhesion between the aluminum and titanium layers was obtained byminimizing the corrosion of the aluminum layer. Corrosion is largely aresult of exposure of the aluminum layer to chlorine ions (Cl⁻) releasedfrom titanium tetrachloride (TiCl₄) during deposition. By reducing theflow rate of titanium tetrachloride, the corrosion of the aluminum layeris reduced and adhesion is improved. Reduced titanium tetrachloride flowalso reduces the deposition rate, allowing dissociated titanium atomsadditional time to locate stable sites in the underlying aluminum layer.This additional time is particularly needed due to the low thermalenergy and reduced thermal motion of the titanium atoms at reducedprocess temperatures.

The deposition runs of Table 13 were made at further reduced TiCl₄ flowrates. All of the wafers of Table 13 were thermal oxide. None of thewafers of Table 12 or 13 were annealed with an NH₃ RF anneal.

Deposition Parameters for Table No. 13

TiCl₄ (sccm) wafers 1-2, 4 sccm; 3-4, 3 sccm; 5-6, 2 sccm; and wafer 7at 1 sccm

H₂ (sccm) 3,750

RF Power (watts) 250 @ 450 KHz

Reaction Chamber Pressure (Torr) 5

Susceptor Rotation Rate (rpm) 100

Deposition time (sec) 300 (wafers 1 and 2 at 180 and 240, respectively)

Substrate Temperature (°C.) approximately 400° C.

Susceptor Temperature (°C.)

                  TABLE NO. 13    ______________________________________    Results and    Additional             WAFER NO.    Parameters             1      2       3    4     5    6     7    ______________________________________    TiN layer             89     132     158  149   158  166   407    thickness    (Å)    Deposition             30     33      32   32    32   33    21    Rate    (Å/min)    Layer    259    239     199  199   190  208   482    Resistivity    (μΩ-cm)    ______________________________________

Discussion of Results from Deposition Runs

Titanium films have ben deposited utilizing the parameters andapparatuses discussed above at rates ranging from 30 Å/min. measured bymass gain and by wave dispersive X-ray fluorescence (WDXRF). It has beenfound that the deposition rate is directly proportional to thedeposition temperature and to the TiCl₄ partial pressure. Filmresistivity increases from 120 to 150 μΩ-cm as the depositiontemperature is decreased from 550° C. to 450° C. Titanium filmsdeposited at 550° C. onto thermally grown oxide were analyzed byRutherford Back Scatter Spectroscopy (RBS) and found to be elementaltitanium. The only impurity that is detectable by RBS is oxygen. AugerElectron Spectroscopy (AES) depth profiling was performed to identifylow level contamination. The AES profiles indicate a bulk chloridecontent of 0.1%. Chloride was also measured by WDXRF, which indicated abulk concentration of 0.45%.

Films were also deposited at 550° C. onto non-deglazed siliconsubstrates. These films were analyzed by RBS and found to have formed asilicide during the deposition process. No post deposition anneal hadbeen performed. The stoichiometry of the in-situ silicided titanium isTiSi₂ but 0.5% chloride was detected. AES depth profiling confirmed thestoichiometry of the in-situ silicide, as well as the bulk chlorinecontent of 0.5%. The AES profiles indicate a low level of oxygen in thesilicide, but there is no evidence of an oxygen peak at thesilicon/TiSi₂ interface. This indicates that the native oxide has beenremoved by the CVD-Ti process.

Titanium films were deposited at 550° C. onto patternedborophospho-silicate glass (BPSG) in order to observe film conformality.All contacts were 1 μm to 0.35 μm (aspect ratios varied from 1.0 to2.9). The titanium films were found to be conformal for all aspectratios. Film thicknesses of up to 1500 Å were deposited and crosssections were observed by a scanning electron microscope (SEM). Therewas no evidence of overhang formation at the contact openings. Overhangformation is a fundamental problem with line of sight depositionprocesses such as sputtering. This problem has been well documented forboth conventional and collimated sputtering, and the conformal nature ofthe CVD-Ti process represents a significant advantage over sputteringtechnology.

A comparison of the electrical properties obtained with CVD-Ti andsputtered-Ti was made using the electrical test structures describedabove. Contact resistance measurements were made using Kelvin structureswith contact sizes which varied from 0.35 μm to 0.60 μm. In order todeposit 100 Å of titanium at the bottoms of the 0.35 μm contacts, 900 Åof sputtered-Ti was deposited compared to 200 Å of CVD-Ti. The CVD-Tiand sputtered-Ti films provided equivalent contact resistance for allcontact sizes. However, the smaller contacts had a much higher probeyield with the CVD-Ti contact layer. For 0.35 μm contacts the yield forthe CVD-Ti contact layer was double that of the sputtered-Ti layer. Theimprovement in yield indicates that the CVD-Ti process provides moreuniform and repeatable results over the surface of the wafer, andsuggests that the process may overcome minor contact to contactvariations that are created by the contact etch and contact cleaningprocesses. This assertion is supported by the AES results reported abovewhich showed that no residual native oxide was detected at thesilicon/TiSi₂ interface after CVD-Ti and in-situ silicidation.

A more severe comparison of the two contact layers was made using chainsof 10,000 contacts. Again the results were similar for the largercontacts. However at 0.35 μm The CVD contact layer produced superiorresults. The CVD-Ti contact layer provides contact chain resistancevalues that are two orders of magnitude lower than those obtained withthe sputtered-Ti layer. Furthermore, the probe yield for the CVD-TIlayer was five times higher than that for the sputtered layer.

Leakage current measurements for CVD-Ti and sputtered-Ti were similar.This indicates that the in-situ silicidation provided by the CVD-Tiprocess does not cause junction damage. This is confirmed by SEM crosssections which were performed on the samples after completing theelectrical measurements. The cross sections confirm that the silicideformed during the CVD-Ti process at the bottoms of the contacts isuniform.

In conclusion, titanium films have been deposited by chemical vapordeposition at temperatures of 450° C. to 550° C. The titanium is fullyconverted to TiSi₂ during the deposition process for depositions ontosilicon surfaces. Depositions were conformal with no evidence oftitanium overhangs at contact openings. Contact resistance and junctionleakage measurements indicate that the CVD-Ti process providesequivalent electrical performance to sputtered-Ti for low aspect ratiofeatures. For higher aspect ratio features the CVD-Ti process providessuperior contact resistance and yield. The improvement in electricalperformance is due to the conformal nature of the CVD-Ti, the removal ofthe residual native oxide from the contact bottom, and formation of auniform TiSi₂ layer at the contact bottom.

FIG. 3 shows another embodiment of a deposition chamber with an upstreamRF plasma source which might be utilized to generate the necessaryradicals for an upstream plasma low temperature PECVD process utilizinga rotating susceptor as discussed and disclosed hereinabove with respectto the upstream plasma generation utilized by the configuration ofFIG. 1. Specifically, a deposition chamber 280 is attached to an RFplasma source 282. A suitable source is a commercially available RFsource available from Prototech Research, Inc., of Tempe, Ariz. RFplasma source 282 includes a housing 284 which forms a plasma generatingregion 286 therein. The plasma gases to be excited, such as H₂, N₂,and/or NH₃ are introduced through gas input lines 287, 288 and gas rings289, 290, respectively. Within region 286, the plasma gases are excitedby an RF field generated by RF coil 292 which is connected to an RFsource 294. RF energy of, for example, approximately 13.56 MHZ isdelivered to the gases within region 286 to create a gas plasmacontaining free electrons, ions and radicals of the plasma gas. As theexcited gases are drawn down the length of plasma-generating region 286,gas particles combine until preferably an abundance of radicals remain.The radicals are drawn down through a deposition region 296. Thereactant gases, such as TiCl₄, are introduced into the deposition region296 by a vertically adjustable gas showerhead 298, and the reactantgases and activated radicals are drawn down to substrate 300 by rotatingsusceptor 302 and combine to form a film layer on substrate 300. Thesubstrate 300 heated as discussed above and similar pressures, susceptorrotation rates and gas flow rates for the examples discussed above mightbe utilized with the RF plasma source of FIG. 3. Accordingly, a film,such as a titanium-containing film, may be deposited at substantiallylower temperatures than achieved with traditional thermal CVD processes.

While the present invention has been illustrated by the description ofembodiments thereof, and while the embodiments have been described inconsiderable detail, it is not the intention of Applicants to restrictor in any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. For example, the low temperature CVD technique ofthe present invention may be utilized to deposit other films besides thetitanium-containing films discussed in extensive detail herein.Furthermore, activated radicals of gases other than H₂, N₂ and/or NH₃might also be utilized to lower the deposition temperature. Theinvention in its broader aspects is therefore not limited to thespecific details, representative apparatus and method, and illustrativeexample shown and described. Accordingly, departures may be made fromsuch details without departing from the spirit or scope of Applicants'general inventive concept.

What is claimed is:
 1. A method of depositing a film on a substratelocated in a chemical vapor deposition reaction chamber by plasmaenhanced chemical vapor deposition comprising:providing a substrateinside a chemical vapor deposition reaction chamber; supplying a firstgas for introduction into said reaction chamber; biasing agas-dispersing showerhead in said chamber with an RF energy source sothat the showerhead acts as an RF electrode with an associated RF field;directing the first gas through a plurality of openings in saidshowerhead and through the RF field to excite said first gas to formactivated radicals and ions of the first gas proximate the substrate;supplying a second gas including a titanium tetrahalide constituent intosaid reaction chamber to mix with the first gas radicals and ions;spacing the biased showerhead approximately one inch or less from thesubstrate inside said reaction chamber for providing a concentrateddensity of the activated radicals and ions to react with the second gasin a surface reaction on a surface of said substrate to deposit the filmon said substrate surface.
 2. The method of claim 1 furthercomprising:rotating said substrate to draw the mixture of the first gasradicals and ions and the second gas to the substrate surface to promoteuniform deposition of the film on the substrate surface.
 3. The methodof claim 1 further comprising:passing said first gas through a cylindercoupled to the showerhead above the substrate to establish a first gasflow before passing the first gas through the showerhead, whereby toproduce a uniform flow of radicals and ions to said substrate.
 4. Themethod of claim 1 further comprising exciting said second gas with saidshowerhead and RF field such that the gas mixture contains first gasradicals and excited gas particles of the second gas.
 5. The method ofclaim 1, wherein the first gas is selected from the group consisting ofhydrogen, nitrogen, ammonia and mixtures thereof.
 6. The method of claim1, wherein a diluent gas is mixed with said first gas.
 7. The method ofclaim 6, wherein said diluent gas includes argon.
 8. The method of claim2 further comprising rotating said substrate at a rate sufficient toproduce a laminar flow of the first and second gas mixture over thesubstrate to reduce gas recirculations and recombinations of theactivated radicals and ions.
 9. The method of claim 1 further comprisingheating the substrate between 200° C. and 800° C. during deposition ofthe film.
 10. The method of claim 1 further comprising maintaining thepressure inside the reaction chamber between 0.5 and 15 Torr.
 11. Themethod of claim 2 further comprising rotating the substrate at a ratebetween 0 and 50,000 rpm.
 12. The method of claim 1 further comprisingsupplying the first gas at a rate between 50 and 50,000 sccm.
 13. Themethod of claim 1 further comprising supplying the second gas at a ratebetween 1 and 20 sccm.